Disable NCO/Mixer on AD9625

In our application we want to use two AD9625 devices to digitize the IQ baseband output of an analog quadrature demodulator and enable the decimation filters on the AD9625 to reduce the amount of data transferred over the JESD204B interface as there are not enough lanes available to drive 2 AD9625 devices at full rate. On the AD9680 it is possible to bypass the NCO mixer in the DDC, but the AD9625 does not appear to offer a similar function. Is there a way to bypass the NCO mixer on the AD9625 so that it outputs only the real portion of the decimated signal?

In the absence of a specific zero-IF mode it seems that it should be possible to set the NCO phase accumulator to zero which would center the down-conversion at DC. Would this have the desired effect? The AD9625 would still be outputting I and Q data but the Q data could simply be discarded and what would remain would be the I data from each AD9625 device which could be re-assembled into the IQ signal from the analog mixer.

Additionally, is there support for the DDC modes in the AD-FMCADC2-EBZ linux driver that could be used to evaluate the performance of these features?

Please redirect your question about the IIO oscilloscope application to the FPGA Reference Designs forum, where the FPGA software team can better help answer your questions.

The NCO in the AD9625 sets the mixer frequency of the DDC. For a setting of zero, the decimation filter essentially acts as low pass half band since the effective NCO frequency is 0Hz. For example, when sampling at 2,000MSPS using dec/8 and NCO=0, the total complex BW would be 250MHZ with the pass-band of the half band filter from 0 to 125Mhz. The effective BW would be slightly less than the total BW (~90%) since the filter is not an ideal "brick".

Please redirect your question about the IIO oscilloscope application to the FPGA Reference Designs forum, where the FPGA software team can better help answer your questions.

The NCO in the AD9625 sets the mixer frequency of the DDC. For a setting of zero, the decimation filter essentially acts as low pass half band since the effective NCO frequency is 0Hz. For example, when sampling at 2,000MSPS using dec/8 and NCO=0, the total complex BW would be 250MHZ with the pass-band of the half band filter from 0 to 125Mhz. The effective BW would be slightly less than the total BW (~90%) since the filter is not an ideal "brick".